1. Field of the Invention
The present invention relates to a process for producing a single crystal semiconductor layer by recrystallizing a polycrystalline or amorphous semiconductor layer provided on a single crystal semiconductor substrate, with an insulator layer having an opening part provided therebetween, and a semiconductor device such as a diode, a transistor and a thyristor, which comprises a single crystal semiconductor layer produced by the process as a base. In particular, the invention relates to a process by which a polycrystalline or amorphous semiconductor layer can be recrystallized to be a single crystal semiconductor layer with high quality and in a wide range by scanning irradiation with an energy beam controlled in power and temperature distribution while using as a seed a single crystal semiconductor substrate making contact with the semiconductor layer through an opening part, and a semiconductor device comprising a single crystal semiconductor layer with high quality and wide range which is produced by the process.
2. Description of the Prior Art
In recent years, to accomplish increases in the speed and density of semiconductor device, there has been an attempt to produce the so-called three-dimensional semiconductor integrated circuit device in which floating capacitance can be reduced by electrically separating semiconductor circuit elements by dielectric and flat form circuit elements in a three-dimensional manner. In a method, first, a polycrystalline or amorphous semiconductor layer is laminated on the above-mentioned single crystal semiconductor substrate, with an insulator layer having an opening part provided therebetween. Next, the polycrystalline or amorphous semiconductor layer is irradiated with an energy beam to melt, and recrystallize, the polycrystalline or amorphous semiconductor layer. In the recrystallization, since the polycrystalline or amorphous semiconductor layer is in contact with the semiconductor single crystal of the substrate through the opening part, the single crystal serves as a seed for formation of the single crystal semiconductor layer. The single crystal semiconductor layer produced by this method has been provided with the above-mentioned semiconductor circuit elements such as diodes and transistors.
An example of the process for producing the so-called three-dimensional semiconductor device comprising a single crystal semiconductor layer provided with the semiconductor circuit elements mentioned above is "Single Crystal Silicon-on-Oxide by a Scanning CW Laser Induced Lateral Seeding process" presented by H. W. Lain et al in "J. Electrochem. Soc.: SOLID-STATE SCIENCE AND TECHNOLOGY" vol. 128 (September, 1981), pp. 1981-1986. According to the prior art literature, a single crystal is grown from a polycrystalline or amorphous silicon by using a single crystal of substrate silicon as a seed, to thereby contrive recrystallization.
FIG. 1 shows a cross-sectional view of a semiconductor device produced by the above-mentioned lateral seeding process disclosed as prior art. In the figure, on a major surface of a single crystal silicon substrate (hereinafter referred to simply as "substrate") 1 as a single crystal semiconductor substrate is provided an oxide insulator layer (hereinafter referred to simply as "insulator layer") 2 consisting of, for example, silicon dioxide. The insulator layer 2 does not cover the entire part of the major surface of the substrate 1, that is, a portion of the major surface is exposed through opening parts 3. Polycrystalline silicon 4P is laminated as a thin film layer 4 on the entire part on the surface side of the insulator layer 2 and the opening parts 3. Therefore, the polycrystalline silicon 4P is in contact with single crystal silicon 1S of the substrate 1 through the opening parts 3. Next, while irradiating the polycrystalline silicon 4P with a laser beam 5 used as an energy beam, the laser beam 5 is scanned in the direction of arrow X, whereby the polycrystalline silicon 4P is melted to be a molten portion 4M, and when the polycrystalline silicon 4P of the molten portion 4M is resolidified, silicon is recrystallized and grows as single crystal silicon 4S while the single crystal silicon 1S of the substrate 1 making contact therewith through the opening part 3 serves as a seed.
The lateral seeding process has been deemed an ideal crystal growth technique, since the crystal orientation of the single crystal silicon 4S of the thin silicon film layer 4 is perfectly determined by the single crystal silicon 1S of the substrate 1. In addition, a technical idea similar to the above process is disclosed in the patent application entitled "Process for Forming Single Crystal of Semiconductor" which has been applied by Hitachi, Ltd. and published by Japanese Patent Office as Japanese Patent Publication No. 42-12087 (1967) on Jul. 10, 1967.
However, though thought to be excellent in principle, this process has not succeeded in practice. Namely, the crystal growth of a thin silicon film layer 4 using the single crystal silicon 1S of the substrate 1 as a seed proceeded only to about 100 to 200 .mu.m from the opening part 3, and a multiplicity of crystalline defects such as stacking faults and twins were generated, so that a favorable single crystal layer was not formed. The reason for the ill success of the above-mentioned lateral seeding process lies in that no device has been made to compensate for the laser beam power distribution, which is approximate to the Gaussian distribution, in the scanning irradiation with the laser beam to melt and re-solidify the semiconductor formed of silicon or the like. In FIGS. 2A to 2C in which the same reference symbols as those in FIG. 1 denote the same or corresponding parts, the region irradiated with the laser beam 5 shows a temperature distribution as shown in FIG. 2A, in a direction crossing the beam scanning direction (arrow X). FIG. 2B is a plan view of the condition where the region of the temperature as shown in FIG. 2A has moved on the thin silicon film layer 4, and is presented in comparison with FIG. 2C which is a cross-sectional view corresponding to FIG. 1. In the figure, when the laser beam 5 is moved in the direction of hollow arrow X, a single crystal 4S in the thin silicon film layer 4 grows in the directions of the multiplicity of fine arrows. The directions of the fine arrows extend from low temperature portions at both side edges with respect to the moving direction of the laser beam 5 toward the center axis O of the scanning zone. Since the directions of crystal growth from the side edges meet each other in the manner of conforming substantially to the center axis O, the subsequent growth of the region of single crystal silicon 4S seeded at the opening part 3 and grown to be a single crystal (the hatched area in FIG. 2B) is inhibited. The length over which the region of the single crystal silicon 4S extended is 100 to 200 .mu.m, as mentioned above.
To prevent the crystal growth from proceeding in the directions of the fine arrows from both side edge parts of the scanning zone of the laser beam as mentioned above, an attempt has been made to provide an anti-reflection film or reflective film in a striped form on the face side of the thin film layer 4. An example of this is the anti-reflection film or the like disclosed in "Use of selective annealing for growing very large grain silicon on insulator films" presented by J. P. Colinge et al in "American Institute of Physics/Appl. Phys, Lett. 41(4), Aug. 15, 1982".
FIGS. 3A to 3C respectively show a partly enlarged plan view of a semiconductor device provided with the above-mentioned anti-reflection film on the surface of a thin silicon film layer, a cross-sectional view taken on line B--B of FIG. 3A and a cross-sectional view taken on line C--C of FIG. 3A, in which the same symbols as those in FIG. 1 and FIGS. 2A to 2C denote the same or corresponding parts. In each of the figures, an anti-reflection film 6 comprises anti-reflection zones 6a provided at positions corresponding to an insulator layer 2 of a substrate 1 and stripe portions 6b each provided between the anti-reflection zones 6a in the scanning direction X of a laser beam 5, and is constituted of, for example, a silicon nitride film.
The detailed construction of a semiconductor device 7 comprising the above-mentioned anti-reflection film 6 will now be explained. The substrate 1 consists of single crystal silicon 1S having a {001} plane--a (100) plane or an equivalent crystal plane--as a major surface, and a relatively thick insulator layer 2 constituted of silicon dioxide and having an elongate opening part 3 reaching the major surface of the substrate 1 at least at a part thereof is provided on the major surface of the substrate 1. The opening part 3 is provided in a &lt;110&gt; direction or an equivalent direction (hereinafter referred to simply as "&lt;110&gt; direction") on the major surface of the substrate 1. The thin film layer 4 constituted of polycrystalline silicon 4P is formed by a chemical vapor deposition method (hereinafter referred to as "CVD method"). The striped anti-reflection film 6 comprises stripe portions 6b the longitudinal direction of which is set in the &lt;110&gt; direction (precisely, the &lt;110&gt; direction), and is built up in a film thickness of 550 .ANG. by the CVD method, in order to control the temperature distribution in the polycrystalline silicon 4P at the time of irradiation with the laser beam 5. The laser beam 5 is scanned in the direction of hollow arrow X in FIGS. 3A and 3B, namely, the &lt;110&gt; direction.
Now, the method of providing a single crystal semiconductor laser through crystal growth on the insulator layer 2 constituted of a relatively thick oxide film will be explained. First, the polycrystalline silicon 4P on the elongate opening part 3 and the relatively thick insulator layer 2 is melted by irradiation with the laser beam to form a molten portion 4M, the melting being caused to reach to the major surface of the substrate 1 at the opening part 3. As a result, the molten part 4M starts epitaxial growth with the single crystal silicon 1S of the substrate 1 as a seed crystal, and the thin silicon layer 4 is recrystallized from polycrystalline silicon 4P into single crystal silicon 4S. Therefore, when the laser beam 5 is scanned in the direction of arrow X--precisely, in the &lt;110&gt; direction on the major surface of the substrate 1--during the irradiation, the molten portion 4M is set into epitaxial growth along the plane orientation of the major surface of the substrate 1, and the single crystal silicon 4S is formed to extend on the insulator layer 2. In this case, the striped anti-reflection film 6 provided on the thin silicon film layer 4 raises the temperature in the transverse direction with respect to the scanning direction of the laser beam 5. Namely, the temperature of polycrystalline silicon 4P under the region where the anti-reflection film 6 is provided as anti-reflection zones 6a and stripe portions 6b is higher than the temperature of polycrystalline silicon 4P under the region where the anti-reflection zones 6a and the stripe portions 6b are not provided. Accordingly, a periodical temperature distribution in the transverse direction--with respect to the scanning direction--is developed in the region irradiated with the laser beam 5, and in recrystallization of the molten portion 4M, only epitaxial crystal growth takes place with the single crystal silicon 1S at the opening part 3 as a seed crystal. The laser beam 5 is scanned over the entire surface of the thin film layer 4 of the polycrystalline silicon 4P, whereby the single crystal silicon 4S is formed over the entire region of the surface of the semiconductor device 7. Thereafter, the anti-reflection film 6 constituted of a silicon nitride film or the like is removed, resulting in the condition where semiconductor integrated circuit elements such as transistors and diodes can be provided on the single crystal silicon 4S on the surface of the semiconductor device 7.
However, the process for producing a single crystal semiconductor layer using the anti-reflection film mentioned above and the semiconductor device produced by the process has the following various problems.
First, since the laser beam 5 is scanned in direction X orthogonal to the elongate opening part 3 of the insulator layer 2 (precisely, in the &lt;110&gt; direction with respect to the major surface), the liquid-solid interface does not accord with the shape of the (111) plane constituting the crystal growth plane. Therefore, the epitaxial growth is stopped at a distance of about 100 to 200 .mu.m from the opening part 3, after which a crystal having other crystallographic axes would grow. Accordingly, it has been impossible to produce a single crystal semiconductor layer with high quality and wide range.
To solve the above problems, attempts may be made to increase the distance of epitaxial growth of the single crystal on the insulator layer by making the shapes of the liquid-solid interface and the (111) plane accord with each other. As one of such attempts, a method may be contemplated in which the longitudinal direction of the stripe portions of the anti-reflective film constituted of silicon nitride is set to be coincident with or approximate to the &lt;100&gt; direction and the laser beam is scanned during irradiation therewith in a direction parallel to the longitudinal direction of the stripe portions. However, even when the laser beam is scanned in such a direction that the liquid-solid interface accords with the shape of the (111) plane, the crystal state on the left side of the molten portion 4M of the polycrystalline silicon 4P is different from that on the right side--namely, silicon is already in the state of single crystal silicon 4S on one side but it remains as polycrystalline silicon 4P on the other side--, so that the thermal conductivity of silicon varies in the vicinity of the molten portion 4M of the thin film layer 4, resulting in that the shape of the liquid-solid interface becomes irregular. The irregularity of the shape of the liquid-solid interface in the thin film layer hinders the epitaxial growth of single crystal of the semiconductor layer constituted of silicon or the like. As a counter-measure to this problem, use of a lower scanning speed of the energy beam such as a laser beam to stabilize the liquid-solid interface may be contemplated, but such an approach is unsatisfactory because the crystal growth cannot thereby be improved fundamentally.
Further, in the case of the above-mentioned disaccord of the liquid-solid interface in the thin silicon film layer 4 with the shape of the (111) plane constituting the crystal growth plane, a force such as to make the (111) plane accord with the liquid-solid interface acts in the thin film layer 4. Such an irrational force on or near the crystal growth plane causes crystalline defects such as stacking faults in the semiconductor layer such as the thin silicon layer 4. As a result, as mentioned above, the epitaxial growth of the semiconductor layer would be stopped at a distance of about 100 to 200 .mu.m, and crystals having crystallographic axes different from those of the semiconductor converted into a single crystal would grow, leading to poor quality of the semiconductor device.
A description that the stable crystal growth takes place on (111) plane as mentioned above is found also in "Zone-Melting Recrystallization of Si Film with a Moveable-Strip-Heater Oven" presented by H. W. Geis et al in "J. Electrochem. Soc.: SOLID-STATE SCIENCE AND TECHNOLOGY, December 1982", pp. 2812-2818 (Refer particularly to FIG. 7).